1. Field of the Invention
This invention relates to water-cooled nuclear reactors, and more particularly to pressurized water reactors having in-core instrumentation that enter the reactor vessel through penetrations from the top of the reactor vessel and are used to monitor the neutron activities and coolant temperature within the core fuel assemblies.
2. Description of the Prior Art
Many water-cooled nuclear reactors utilize a core of vertically-positioned fuel assemblies within a reactor vessel. To monitor the neutron activities and coolant temperature within the core fuel assemblies, movable in-core instrumentation, such as movable neutron detectors, conventionally enter the core from penetrations in the bottom of the vessel. In a few instances in the past leakage occurred at the penetrations at the bottom of the vessel which presented significant repair problems. Accordingly, it would be desirable to have all the in-core instrumentation access the core through penetrations from the top of the reactor vessel.
Thus, it is therefore necessary to provide structure which can satisfactorily guide and protect the in-core instrumentation entering from the top of the vessel and mitigate the potential for leakage.
To provide guidance and protection for the in-core instrumentation the upper core plate, which is just above the fuel assemblies, upward to the penetrations through the vessel head, the existing upper support columns are available in-between the upper core plate and the upper support assembly. What is needed is a structure which provides guidance and protection for the in-core instrumentation in the elevations between the upper support assembly and the penetrations in the vessel head.